The use of antimicrobial agents plays an important part in current medical therapy. This is particularly true in the fields of dermatology as well as skin and wound antisepsis, where the most effective course of treatment for skin or mucous membranes, which are afflicted with bacterial, fungal, or viral infections or lesions, frequently includes the use of a topical antimicrobial agent, such as antibiotics. For decades medicine has relied primarily upon antibiotics to fight systemic as well as topical infections.
Antibiotics are organic molecules produced by microorganisms that have the capacity in dilute solutions (e.g., solutions less than 10 μg/ml and often less than 1 μg/ml) to destroy or inhibit the growth of bacteria and other microorganisms. They are generally effective at very low levels and are often safe with very few, if any, side effects. Antibiotics are commonly of a narrow spectrum of antimicrobial activity. Furthermore, they often act on very specific sites in cell membranes or on very specific metabolic pathways. This can tend to make it relatively easy for bacteria to develop resistance to the antibiotic(s) (i.e., the genetically acquired ability to tolerate much higher concentrations of antibiotic) either through natural selection, transmission of plasmids encoding resistance, mutation, or by other means. Not only does resistance eliminate the ability of a medication to treat an affliction, but it can also put the patient at further risk, especially if the antibiotic is one that is routinely used systemically.
In the past few decades it has become well established that colonization of the anterior nares with Staphylococcus aureus (SA) can lead to multiple problems. Medicine has relied primarily upon antibiotics for nasal decolonization. For example, bacitracin, neomycin sulfate, polymyxin B sulfate, gentamicin, framycetin-gramicidin, lysostaphin, methicillin, rifampin, tobramycin, nystatin, mupirocin, and combinations thereof, have been used with varying success for nasal decolonization.
For example, nasal colonization with SA in presurgical patients has resulted in higher infection rates and higher rates of other nosocomial infections such as catheter infections. Nasal colonization with SA in hemodialysis patients has resulted in a much higher incidence of blood stream infections. Furthermore, it has been well established that the anterior nares is the ecological niche for SA colonization and thus spread of methicillin resistant staphylococcus aureus (MRSA) in a hospital or other health care facilities in the event of an outbreak can be mitigated by decolonizing the anterior nares of patients and healthcare workers.
Mupirocin, marketed as the calcium salt in Bactroban Nasal by Glaxo Smith Kline, is the only antibiotic approved by the Food and Drug Administration for nasal decolonization use in the United States. For example, there are multiple reports of resistance to mupirocin when used as a nasal decolonizing agent. Resistance rates have been reported as high as 25% and even as high as 50% (see, for example, E. Perez-Roth et al., Diag. Micro. Infect. Dis., 43:123-128 (2002) and H. Watanabe et al., J. Clin. Micro., 39(10): 3775-3777 (2001)). Even though presurgical decolonization of the anterior nares using mupirocin has been shown to decrease the risk of surgical site infection by as much as 2 to 10 times (T. Perl et al., Ann. Pharmacother., 32:S7-S16 (1998)), the high resistance rates to this antibiotic make it unsuitable for routine use.
Antiseptics, on the other hand, are synthetic molecules that destroy or inhibit microorganisms and virus by inhibiting metabolic pathways or altering the cell envelope or both. They tend to have broader spectrum of antimicrobial activity and often act by nonspecific means such as disruption of cell membranes, oxidation of cellular components, denaturation of proteins, etc. This nonspecific activity makes it difficult for microorganisms to develop clinical resistance to antiseptics. For example, there are very few reports of clinical resistance to antiseptics such as iodine, lower alcohols (ethanol, propanol, etc.), chlorhexidine, quaternary amine surfactants, chlorinated phenols, and the like. Some of these compounds, however, need to be used at concentrations that often result in irritation or tissue damage, especially if applied repeatedly. Furthermore, unlike antibiotics, many antiseptics are not active in the presence of high levels of organic compounds. For example, formulations containing iodine or quaternary ammonium compounds have been reported to be inactivated by the presence of organic matter such as that in nasal or vaginal secretions, and perhaps even on skin.
Many antiseptic compounds are viewed as irritants. For example, compositions containing iodine and/or chlorhexidine have been reported to cause skin and mucosal tissue irritation. This is particularly true for sensitive mucosal tissues, such as the anterior nares, nasal and esophageal cavities, which can have a high level of microbial colonization in certain otherwise healthy individuals, as well as individuals with infectious diseases such as chronic sinusitis. Additionally, due to the irritating nature many of these compounds may be unsuitable for application to irritated or infected dermal tissue to treat skin conditions, such as lesions from impetigo and shingles.
Also, for certain applications, especially in the nose and mouth, it is particularly desirable for the compositions to have little or no color, little or no odor, and an acceptable taste. Many antiseptics have undesirable characteristics, such as iodine and iodophors, which have an orange to brown color and a definite odor at concentrations typically employed for antisepsis.
Chlorhexidine gluconate (in combination with neomycin sulfate) has been suggested for use in nasal decolonization with limited success. For example, Naseptin is an antibiotic emulsified cream comprising neomycin sulphate (3250 units/g) and chlorhexidine gluconate (0.1 wt-%) that in combination destroys bacteria. The product also contains arachis oil, cetostearyl alcohol/ethylene oxide concentrate, and cetostearyl alcohol in a water base. The product must be used 4 times/day over 10 days to eradicate nasal carriage of staphylococci. In addition, U.S. Pat. No. 6,214,866 discloses the use of chlorhexidine in combination with the antibiotic mupirocin.
Povidone-iodine has also been suggested for use in nasal decolonization (R. L. Hill and M. W. Casewell, Journal of Hospital Infection, 2000, Vol. 45, 198-205). Betadine Cream (5 wt-% povidone iodine) has been found to kill methicillin resistant staphylococcus aureus in vitro in an enrichment culture technique. Addition of nasal secretions decreased the activity of the povidone-iodine by 80-90% by reaction of the free iodine with the organic load. Other drawbacks of 5% povidone-iodine for use in patients included: 1) a very dark brown color, 2) a low pH, which can cause irritation, 3) a strong iodine odor.
The formulation of components can affect the performance and potential irritation of antimicrobial agents. For example, many conventional antimicrobial compositions are too low in viscosity and/or too hydrophilic in nature to maintain sufficient substantivity and persistence to provide sufficient antimicrobial activity on moist tissue, such as the anterior nares or open, exuding, or infected lesions. It has been reported that the presence of solvents can diminish the antimicrobial activity of many antiseptics. Furthermore, it has been reported that many surfactants can reduce the efficacy of antiseptics by sequestering the antiseptic in micelles. (H. B. Kostenbauer, Chapter 44 in Disinfection, Sterilization, and Preservation, First addition, 1968, C. A. Lawrence and S. S. Block). Additionally, surfactants are often implicated in contributing to irritation.
Thus, there is still a need for effective antimicrobial compositions that develop little resistance and are well tolerated when used on mammalian tissue and especially on moist mammalian tissue such as in the nasal passages, anterior nares, vagina, and wounds.